Fan wheels are commonly used devices for slowing down signatures in a folding machine. Fan wheels comprise a plurality of fan wheel discs defined by a plurality of outwardly projecting curve-shaped fan blades. Fan wheel pockets formed by adjacent blades receive signatures exiting a folding device. The curve shape and jagged surface of the fan blades slow the forward movement of the signatures being deposited in the fan pockets to a complete stop. Once a given fan pocket receiving a signature has turned through approximately 90.degree. the signature is deposited on a delivery system.
A drawback of devices of this nature is that because the signatures enter the fan wheel pockets at such high velocities they are thrust tumultuously against the blades of the fan wheel causing the signatures to tear and otherwise become damaged. Another drawback of these devices is that it is not possible to precisely aim the products towards the bottoms of the fan wheel pockets.
The reason for this is that as the signatures come off belts leading to the fan wheel, a number of factors come into play, such as the paper caliper, the number of pages in the signature, the nature of the paper and even the amount of ink thereon, which will all affect the motion of the signature so that, dependent on the cumulative effect of such factors the signature may land neatly on the bottom of the fan wheel pocket or may recoil backwards or catch on the edge of a fan wheel blade. Once a signature is irregularly positioned on the fan wheel, it will be deposited onto the delivery belt irregularly as well and the product stream thereon is likely to contain laterally displaced, unevenly spaced or skewed signatures. This is especially true where large speed reductions, e.g., (5:1) are required.
U.S. Pat. No. 4,629,175 discloses an apparatus intended to overcome some of these drawbacks. The apparatus comprises a number of rows of grippers rotating between a transfer or supply device and a delivery system. The grippers are slowed down by an acceleration/deceleration drive running in the direction of motion from the transport or supply device to the delivery system from approximately the supply speed to approximately the speed of the delivery system and are able to be accelerated up to the speed they were moving at before such deceleration in the following section of their motion. The grippers are mounted to a cylindrical drum rotating at a constant speed, and the rows of grippers decelerated and accelerated by the deceleration/acceleration drive are turned at a speed equal to that of the drum and are mounted so that they may be shifted in relation to the outer face of the drum.
However, a drawback with this device is that the transfer of the signature from the supply device to the deceleration drum can cause distortion misalignment and/or tearing of the signature. Because this transfer is achieved by positioning the deceleration drum so that the gripper rotates into a position in front of the leading edge of the signature being delivered by the supply device, the velocity of the signature being controlled by the supply device must be greater than the tangential velocity of the gripper on the deceleration drum. This causes the signature to gain on the gripper until it has entered the throat of the gripper a desired distance. The gripper then closes and the velocity of the leading edge of the product abruptly changes to match the velocity of the gripper. If the trailing edge of the signature is in the control of the supply device at this time, then distortion of the signature will occur and possible tearing. A further drawback of this device is that it is not capable of achieving high speed reduction ratios as are now required to accommodate today's new high speed printing presses. This device is designed for speed reduction ratios of approximately 3:1. Speed reduction ratios of 5:1 are now being demanded.